black haw noun 1.: a shrub (Viburnum prunifolium) bearing cymes of white flowers and bluish black drupes 2. a.: southern buckthorn b.: false buckthorn 3.: either of two trees (Bumelia tenax and B. lanuginosa) of the southern United States 4.alsoblack hawthorn: a hawthorn (Crataegus douglasii) of the western United States